STORY HIGHLIGHTS

The town was seized from Islamic State by Iraqi Federal Police units last week as Iraqi government forces

Iraqi security troops said on Monday (November 7) they had found a mass grave containing about 150 decapitated corpses in the town of Hammam al-Alil, south of Mosul.

The town was seized from Islamic State by Iraqi Federal Police units last week as Iraqi government forces, Kurdish Peshmerga and Shi'ite militias backed by U.S.-led air strikes pushed their offensive to recapture Mosul from Islamic State.

The Iraqi police released a video to show the site of the grave.

''These are the corpses of chopped heads, including children, elderly men and women. It is unforgivable crime. Those people are innocent. The Islamic State militants brought them here and killed them," an officer said, speaking at the site.

The UN High Commissioner for Human Rights Ravina Shamdasani said on Tuesday (November 8) she could not confirm media reports of the mass grave, but said it happened to be in the same agricultural college in Hammam al Alil where the U.N. reported the execution of 50 police officers last month.

Islamic State fighters had abducted 295 former Iraqi Security Forces members and forced 1,500 families to retreat with them from the town, she added.

She said it appeared Islamic State either intended to kill them of use them as human shields.